Stent devices are known to the skilled person. They are used to hold open various bodily lumens. Of particular interest to the present invention are stent devices for supporting a wall of a vein or artery. Stent devices can self-expand into a deployed configuration or can be forcibly expanded such as by inflating a balloon within a lumen of the stent device. Self-expanding stent devices can be made of shape memory material. One example of a suitable shape memory material is the shape memory nickel titanium alloy known as Nitinol.
Stent devices may be provided in a number of forms. One example of which has a framework of axially spaced rings of zigzagging struts. The rings are centred on a common axis. The rings are connected to an adjacent ring by several connector struts. When a stent graft is being made, the framework is covered by a liquid impermeable material. The cover may be expanded polytetrafluoroethylene (ePTFE). When a bare stent is being made, the framework is left uncovered.
Generally, a stent device is crimped onto an inner tubular member in a delivery configuration at a distal end of a delivery device. A retaining sheath is disposed coaxially over the stent device to maintain the stent device in the radially reduced delivery configuration. A pull member of some kind is provided for retracting the retaining sheath, thereby leaving the stent device free to expand to the deployed configuration. The pull member is associated with an actuation mechanism provided at a proximal end of the delivery device, perhaps at a handle of the delivery device if one is included, for operation by a medical professional for affecting retraction of the retaining sheath. There is a class of retaining sheaths that are retracted in a “rolling” manner as will be described below. It is with this kind of retaining sheath retraction mechanism that the present is concerned.
Delivery devices having rolling retaining sheaths are known in the prior art. Example prior disclosures can be found in the following patent publications: WO 2007/103666, WO 02/38084, WO 2004/066809, WO 03/002034, WO 86/03398, WO 94/15549, WO 96/32078, WO 2006/020028 and WO 2006/096229, each of which is incorporated by reference in its entirety into this application.
In these prior art disclosures, the retaining sheath is folded back onto itself so as to provide an inner sheath and an outer sheath disposed over the stent device and extending axially along the stent device. A fold portion is formed between the inner sheath and the outer sheath. The inner sheath is attached to the inner member at a position proximal of the stent device. The outer sheath is attached to a pull member. As the pull member is pulled upon and moved axially, the outer sheath moves with it, causing the fold portion to move or “roll” as well. As the fold portion moves with respect to the stent device, the stent device is progressively uncovered from the retaining sheath and is thus free to expand to the deployed configuration.
The rolling mechanism for retracting a retaining sheath is advantageous in a number of ways. A reduced pulling force retraction is provided as compared to withdrawing the retaining sheath by sliding the retaining sheath over the stent device. This can be imagined by comparing the ease with which one rolls a sock off of a foot as compared to trying to slide it off of the foot from the toe end. Thus, problems associated with excessive axial forces on the stent device during sheath retraction are less relevant. Furthermore, it is a retraction method that removes the retaining sheath from the body, as opposed to mechanisms that cut open the sheath and leave it caught between the expanded stent device and an inner sheath of the bodily lumen.
One object of the present invention is to provide a delivery device with a rolling retaining sheath that rolls in a reliable, predictable and low pulling force manner. A yet further objective of the present invention is to provide a delivery device with such a rolling retaining sheath that has a reduced profile in the region where the stent device and the retaining sheath is located.